Embroidered electrode

ABSTRACT

An embroidered electrode ( 10 ) consists of embroidered elements ( 12, 13, 14 ) of electrically conductive thread sewn on a backing material ( 11 ). Within a given element the orientation of stitching is selected to be parallel to the direction in which the element extends.

The present invention relates to fabric electrodes, in particular tofabric electrodes that are of an embroidered construction.

It is known to apply electrodes to a body for either detection ofsignals from the body, for example during electrocardiogrammeasurements, or for application of electrical signals to the body, forexample during muscle, organ or nerve stimulation. Two requirements ofan electrode are that it functions adequately to transfer electricalenergy between the electrode and body and that it is comfortable to thewearer. Making the electrode soft to the touch and flexible can enhancecomfort.

Comfort is especially important during ambulatory use or sports traininguse because it is usually desirable that the wearer is unaware of thepresence of the electrode. In the case of ambulatory use the electrodemay be worn for a long time and in the case of sports training it isimportant that an athlete is not distracted by the presence of theelectrode.

In principle flexible fabric electrodes are capable of offering thecomfort required in ambulatory and sports training applications (as wellas other applications) if suitable materials and construction techniquesare chosen. Furthermore it is possible to incorporate fabric electrodesinto garments as described in WO-A-01/02052 which relates to a garmentadapted to be used as a medical electrode, the garment comprising atleast two different zones with at least one of the zones being anelectro-conductive zone to be used as an electrode, theelectro-conductive zone comprising metal fibres; at least one other ofsaid zones being an elastic zone, being a textile fabric of electricallynon-conductive yarns. The electro-conductive zone may be knitted and theconstruction is described in some detail. WO-A-01/02052 also makes briefmention of the fact that the garment can comprise an elastic zone onwhich an electro-conductive zone is embroidered using electricallyconductive yarns, although little further information is given.

The applicants have experimented with knitted fabric electrodes that aresuitable for performing electrocardiograph (ECG) measurements of a humanunder ambulatory conditions. It is recognised that by using electrodesthat are mechanically flexible they conform to a user to provide addedcomfort and better contact to the skin. Furthermore, if the electrodesare incorporated into a garment and can flex in conformity with thegarment, this can also contribute to user comfort. However, results ofthe experiments have also shown that under ambulatory or sports trainingconditions the use of an electrode that is mechanically flexible cansuffer because the flexing and/or partial stretching of the electrodeduring use has the undesirable effect of generating movement-inducedelectrical noise on the detected ECG measurements obtained using theelectrode. Although the detected signal can be processed to improve theactual ECG signal, in some cases the movement induced noise couldcompletely mask the small electrical ECG signal that is detectable fromthe surface of the skin. The overall effect of the movement inducednoise may be minimised by increasing the content of electricallyconductive material in the electrode-to-skin contact region but this isnot always possible or desirable due to manufacturing limitations or thedetrimental effect on user comfort.

It is an object of the present invention to provide an improvedelectrode having an embroidered element.

In accordance with a first aspect of the present invention there isprovided an electrode including an embroidered element comprisingelectrically conductive thread embroidered onto a backing characterisedin that the element comprises at least one portion in which the threadis stitched with an orientation selected to optimise performance of theelectrode.

Advantageously, local variations in stitch orientation can be used togovern the effective electrical resistance of that electrical elementwhen considered as part of an embroidered pattern.

Optionally, the orientation of the stitching is selected such thatthread direction is substantially parallel with the required directionof electrical conduction. Advantageously this should lead to improvedelectrical conductivity of the element in the direction of electricalconduction.

In accordance with a second aspect of the present invention there isprovided an embroidered electrode comprised of electrically conductivethread stitched on a backing material to form one or more embroideredelement wherein said electrode comprises a primary embroidered elementand one or more further embroidered element extending from a portion ofthe primary element.

Optionally, the primary embroidered element is arranged to loop back onitself.

Optionally, the at least one further embroidered element extends towardsa portion of the primary element.

A portion of one or more of the embroidered elements may be producedfrom the electrically conductive thread that is stitched with anorientation selected to optimise performance of the electrode.Preferably the orientation of the stitching is selected such that threaddirection is substantially parallel with the required direction ofelectrical conduction in the locality of the portion.

In one possible arrangement, the primary embroidered element forms aperipheral electrode component and at least one of the furtherembroidered elements extends within the periphery described by theperipheral component from one portion of the primary element to anotherportion of the primary element. In this case at least one of the furtherembroidered elements may intersect and cross over another one of thefurther embroidered elements.

The electrically conductive thread may be silverised polyamide.

In accordance with a third aspect of the present invention there isprovided a garment or accessory comprising an embroidered electrode ofthe first or second aspect.

In accordance with a fourth aspect of the present invention there isprovided a device comprising an embroidered electrode of the first orsecond aspect.

These an other aspects of the present invention will now be describedwith reference to the Figures of the accompanying drawings in which:

FIG. 1 shows a front view of a first embodiment of an embroideredelectrode of the present invention; and

FIGS. 2 a to 2 c show alternative embroidering patterns of furtherembodiments of embroidered electrodes of the present invention.

It should be noted that the drawings are diagrammatic and not drawn toscale. Relative dimensions and proportions of parts of the Figures havebeen shown exaggerated or reduced in size for the sake of clarity andconvenience in the drawings. The same reference signs are generally usedto refer to corresponding or similar features in the differentembodiments.

An embroidered electrode 10 is formed by an embroidering process inwhich electrically conductive thread is attached onto a backing material11 by stitching the thread in a pattern. At least the exterior surfaceof the thread should be electrically conductive. The backing material isnon-conductive felt sheet. In the case of the embroidered electrode 10the embroidered pattern consists of a first embroidered element 12 thatis generally oval in shape and continuous to form a peripheral componentof the electrode 10. The embroidered pattern also consists of furtherembroidered elements in the form of a first plurality of substantiallylinear elements 13 that run parallel to each other and are spaced apartfrom each other to extend within the peripheral component from a portionof the first element 12 to another portion of it. In the arrangementshown, each linear element 13 of the first plurality extends from and toa different part of the peripheral component formed by first element 12.The embroidered pattern also consists of further embroidered elements inthe form of a second plurality of substantially linear elements 14 thatrun parallel to each other and are spaced apart from each other toextend within the peripheral component from a portion of the firstelement 12 to another portion of it. In the arrangement shown, eachlinear element 14 of the second plurality extends from and to adifferent part of the peripheral component formed by first element 12.The first plurality of substantially linear elements 13 extend in adirection that is substantially 90 degrees to the direction that thesecond plurality of substantially linear elements 14 extend. When theelectrode is arranged to be viewed such that the major axis of the ovaldescribed by the first embroidered element 12 is horizontal and deemedto extend in a direction of zero degrees, the first plurality ofsubstantially linear elements 13 extend in a direction of +45 degrees tothe major axis and the second plurality of substantially linear elements14 extend in a direction of +135 degrees to the major axis.

The applicants have recognised that the process of embroidering permitsthe stitch direction (orientation) to be chosen at will in the localityof the stitching. Therefore unlike a knitting or weaving process whichplaces a restriction on the direction of woven or knitted yarn, theembroidery process permits stitch direction to be selected at aparticular locality of an embroidered pattern independently of thestitch direction selected at any other locality of the embroideredpattern. The applicants have also recognised that when embroidering bystitching with an electrically conductive thread good electricalconductivity is provided along the thread and so therefore goodelectrical conductivity in a particular locality of an embroideredpattern will be obtained in the direction of the stitch orientation.Therefore, for a given embroidered pattern the careful choice of stitchdirection in various localities of the pattern can be used to controlthe electrical conductivity of the embroidered pattern. In the case ofan embroidered pattern forming an electrode the stitch direction willnormally be selected in various localities of the pattern to optimiseelectrical conductivity of the pattern overall.

The applicants have also recognised that when an attempt is made tostretch a portion of an embroidered pattern in a direction parallel to(i.e. along) the portions' stitch direction the change in electricalconductivity is low in comparison to when the portion is stretched in adirection that is not parallel to the portions stitch direction. This isthought to be because the main mechanism of electrical conduction alongstitch direction is via the electrically conductive thread whereas themain mechanism of conduction in a direction orthogonal to the stitchdirection will rely on inter-thread contact, the effectiveness of suchcontact being susceptible to stretching and flexing of the embroideredportion because contact between adjacent conductive threads is beingdisturbed. If the change in electrical conductivity is low whenstretched or flexed then the associated movement induced electricalnoise observed when measuring biometric signals using an electrodehaving an embroidered pattern of electrically conductive material isalso advantageously low. The embroidered electrode is generallyresistant to stretch by nature of it being embroidered although duringuse it is possible for small amounts of stretch to occur.

The stitch direction of the first plurality of substantially linearelements 13 is parallel to the direction in which those linear elements13 extend. Therefore, if an attempt is made to stretch the sensor in adirection that is parallel to the direction of the first plurality ofsubstantially linear elements 13, denoted by line A-A, the change inelectrical resistance along the length of a linear element will besmall, typically in the order of less than one tenth of an ohm. Thestitch direction of the second plurality of substantially linearelements 14 is parallel to the direction in which those elements extend.Therefore, if an attempt is made to stretch the sensor in a directionthat is parallel to the direction of the second plurality ofsubstantially linear elements 14, denoted by line B-B, the change inelectrical resistance along the length of a linear element will besmall, typically in the order of less than one tenth of an ohm.

When the electrode is stretched in a direction different to A-A or B-Bwhere will still be adequate conduction along conductive stitched yarnthat makes up the electrode pattern which helps to minimise the changeof electrical properties, hence limit electrically induced noise.

Optionally further embroidered elements may be added to the embroideredpattern to run in a direction different to the first plurality 13 andsecond plurality 14 of elements.

For example, with reference to FIG. 1 a further plurality of elementscould run in a direction (denoted X) parallel to the major axis of theoval described by the peripheral component 10 and/or further pluralityof elements could run in a direction (denoted Y) which is parallel tothe minor axis described by the peripheral component 10.

The process of embroidering is well known to the person skilled in theart, the process consisting of stitching thread to a backing material 11to build up an embroidered pattern. Two threads are used in thestitching process—one thread being predominantly situated on a firstsurface of an embroidered backing material and another thread beingpredominantly situated on a second (opposite) surface of the backingmaterial, one thread being interlooped with the other thread by virtueof the stitching process. In the case of the first embodiment electrode10, the upper surface shown by the plan view of FIG. 1 is the surface ofthe electrode which is worn against the skin during use. Therefore thepattern shown is formed on the upper surface by using electricallyconductive thread. Optionally, the thread stitched on the other surface(not visible) may be conductive or non-conductive: use of conductivethread has the potential to increase electrical conductivity overall butuse of a non-conductive thread will assist where it is necessary toelectrically insulate the electrode on its back-side.

In the case of the first embodiment electrode 10 the electricallyconductive thread is silverised polyamide, although other suitableelectrically conductive threads could be used instead or in addition aswill be appreciated by the person skilled in the art, such as a threadof polyester and stainless steel. Factors which govern the choice ofthread include electrical and physical characteristics of the thread,which are dictated by manufacturing considerations, required comfort ofthe finished electrode during use and whether or not the electrode is tobe washable.

A straightforward DC resistance measurement performed on the firstembodiment electrode 10 comprising embroidered silverised polyamidethread showed that the resistance measured across one end of the firstembroidered element 12 to the other, that is in the direction of themajor axis of the oval, using measuring points denoted ‘C’ and ‘D’ inFIG. 1, was in the region of one ohm, specifically 0.7 ohms. Stretchingor otherwise distorting the electrode gave very little change inelectrical resistance measured and the same measurement under stretchgave a reading of 0.6 ohms.

Where the first plurality of linear elements 13 intersect and cross overthe second plurality of linear elements, they are in physical andtherefore electrical contact with each other by virtue of the stitchingprocess of embroidering. Each of the first and second plurality oflinear elements 13, 14 intersect with the first embroidered element 12that forms the periphery of the electrode: all linear elements are inphysical and therefore electrical contact with the first embroideredelement 12 by virtue of the stitching process.

The electrode 10 is provided with a contact terminal 15 which alsoincludes electrically conductive thread, the contact terminal beingstitched to extend to and establish physical and electrical contact withthe first embroidered element 12. The contact terminal 15 is used toelectrically connect the electrode to electrical or electronicequipment.

The stitch orientation of stitches making up the first embroideredelement 12 is preferably varied around the generally oval shape so thatat a given part of the element 12 the stitches are always in line withthe path taken by the element 12.

During use of the electrode for detecting signals, electrical signalsdetected from a persons skin make their way from the point of detectionof the signal on the electrode through the embroidered pattern by theroute of lowest electrical resistance to electrode contact terminal 15.This route may be via the first embroidered element 12 and/or the first13 and second 14 plurality of electrically conductive elements. Indeed,the signals may zigzag their way via the crossing points of first 13 andsecond 14 electrically conductive elements to contact terminal 15, Byincluding at least one further element running in the direction (denotedX) parallel to the major axis of the oval described by peripheralcomponent 10, say from points denoted in FIG. 1 by C and D, performanceof the electrode in transferring electrical current to or from the bodymay be improved.

The shortest route of least electrical resistance from any point of theembroidered pattern to terminal 15 will generally be the shortest routethrough the pattern, although as already explained the orientation ofthe embroidered stitches in any locality of the embroidered pattern canbe chosen to govern the path of least electrical resistance from oneportion of the embroidered pattern to another, depending on the intendedapplication of the electrode. Indeed, this approach of locally changingstitch orientation can be used to advantage if the intended use of theelectrode is to deliver current to the body, the stitch orientationbeing chosen so that the electrode can distribute current from theelectrode to body more evenly over the area of the electrode than wouldotherwise be the case, and avoid so called ‘hot spots’.

While the first embroidered element 12 is shown to be oval it may assumeother shapes, for example circular, square, rectangular or in the formof some other polygon.

Other embodiments of the electrode are possible without departing fromthe present invention, a selection of which are shown in FIGS. 2 a to 2c. In all cases, at least a portion of the embroidered pattern consistsof stitching that is stitched in a direction substantially parallel,i.e. in line, with the path taken by the embroidered pattern in thelocality of a given stitch. The direction of the shading or dashes inFIGS. 2 a, b, c is intended to indicate stitch direction.

From reading the present disclosure other modifications will be apparentto persons skilled in the art. Such modifications may include otherfeatures which are already known in the design, manufacture and use ofelectrodes, garments or accessories provided with such electrodes,textiles and embroidery and associated manufacture and constructiontechniques and applications thereof and which may be used instead of orin addition to features already described herein.

1. An electrode including an embroidered element comprising electricallyconductive thread embroidered onto a backing characterised in that theelement comprises a first_portion in which the thread is stitched withan orientation such that thread direction is substantially parallel witha first direction of electrical conduction and a second portion in whichthe thread is stitched with an orientation such that thread direction issubstantially parallel with a second direction of electrical conduction,the first and second portions contacting in at least one location.
 2. Anembroidered electrode comprised of electrically conductive threadstitched on a backing material to form one or more embroidered elementwherein said electrode comprises a primary embroidered element and oneor more further embroidered element extending from a portion of theprimary element, wherein the primary embroidered element forms aperipheral electrode component and at least one of the furtherembroidered elements extends within the periphery described by theperipheral component from one portion of the primary element to anotherportion of the primary element.
 3. An embroidered electrode inaccordance with claim 2 wherein the primary embroidered element isarranged to loop back on itself.
 4. An embroidered electrode inaccordance with claim 2 wherein the at least one further embroideredelement extends towards a portion of the primary element.
 5. Anembroidered electrode in accordance with claim 2 wherein a portion ofone or more of the embroidered elements is produced from theelectrically conductive thread which is stitched with an orientationselected to optimise performance of the electrode.
 6. An embroideredelectrode in accordance with claim 2 wherein at least one of the furtherembroidered elements intersects and crosses over another one of thefurther embroidered elements.
 7. An embroidered electrode of claim 5wherein the orientation of the stitching is selected such that threaddirection is substantially parallel with the required direction ofelectrical conduction in the locality of the portion.
 8. An embroideredelectrode in accordance with claim 1 wherein the electrically conductivethread is silverised polyamide.
 9. A garment or accessory comprising anembroidered electrode in accordance with claim
 1. 10. A devicecomprising an embroidered electrode in accordance with claim
 1. 11. Anembroidered electrode in accordance with claim 2 wherein theelectrically conductive thread is silverised polyamide.
 12. A garment oraccessory comprising an embroidered electrode in accordance with claim2.
 13. A device comprising an embroidered electrode in accordance withclaim 2.